Variable resistor



Jan. 15, 1957 M. E. BOURNS 2,777,926

VARIABLE RESISTOR Filed Jan. l2, 1953 2 Sheets-Sheet l v 4| 5/ FQ 'lj/44 40 32 rm 6 3l INVENTOR. MH/FLN E BOU/FNS /7 TTOfF/YEVS Jan. 15, 1957 M. E. BOURNS 2,777,935

VARIABLE RESISTOR Filed Jan. 12, 1953 uw f 2 Sheets-Sheet 2 l ""n `wllllllIllllllllllllllllllllllllIlllllllllllllllllllll United States Patent O VARIABLE RESISTOR Marlan E. Bourns, Riverside, Calif.

Application January 12, 1953, Serial No. 330,642

22 Claims. (Cl. 201-62) This invention relates to variable resistors or potentiometers and more particularly 'to those Which may be easily adjusted to a very accurate degree and which may be built in an extremely small size with high-precision and high-quality materials.

It is, therefore,V the primary object of this invention to provide a new and improved variable resistor which may be easily and accurately adjusted.

lt is a further object of this invention to provide such a variable resistor which may be manufactured in an extremely small size with high-precision and high-quality materials.

It is a further object of this invention to provide a variable resistor which will withstand acceleration, vibration .and extreme ranges of temperature such as those to which vsuch a device may be subjected in aircraft or in guided missile uses.

it is a further object of this invention to provide such a small sized, compact, yet accurate7 variable resistor which has novel means for mounting the same in multiple units.

These and other objects and advantages will be apparent from the annexed specication in which:

Figure l is a perspective view of a resistor manufactured in accordance with one embodiment of the present invennon.

Figure 2 is a perspective view of a plurality of resistors :similar to those shown in Figure 1 mounted in place.

Figure 3 is a section taken along the line 3 3 of 'Figure 1.

Figure 4 is a section taken along the line 4-4 of Figure 3.

Figure 5 is a section taken along theV line 5-5 of Figure 4.

Figure 6 is a section taken along the line 6--6 of Figure 4.

Figure 7 is a perspective of the base element alone.

Figure 8 is a perspective of one of the conductor ele- Figure 9 is a fragmentary section taken along the line -j9-9 of Figure 4.

Figure 10 is an exploded perspective of the block and contact members.

Figure 11 is a top view of an alternative embodiment of the present invention.

Figure 12 is a section taken along the line 12-12 of ,Figure '13.

Figure 13 is a section taken along the line 13-13 of ,Figure l2.

Figure 14 is a perspective elevation of the base member used in the second embodiment.

Figure 15 is a fragmentary perspective elevation of the cover member used in the second embodiment.

Figure 16 is a top view of another embodiment of the present invention.

Figure 17 is a vertical section of the device shown in Figure 16.

Figure 18 is a perspective elevation of the cover used with respect to the tirst embodiment.

rice

Figure 19 is a perspective elevation of the extension embodied in the third embodiment.

Figure 20 is a wiring diagram employed with respect to this invention. i A v i Referring now more particularly to the drawings and particularly to Figures 1 through 10, the variable resistor there illustrated includes a molded plastic base 30 provided with end members 31 and 32 and a bottom member 33 all molded as a single unit. The end members 31 and 32 are provided with reduced portions leaving shoulders 34 and 35, and the bottom portion 33 is reduced to provide a shoulder 36 to receive a metallic cover or cap 37 in the form of a channel-shaped member having a web 38 and flanges 39. Each of the flanges 39 is provided with a pair of holes 40 near the ends thereof and a hollow rivet is provided in each of the holes 40 to hold the cap in place on the base member 30. The end members 31 and 32 are provided with holes 42 adapted to register with the holes 40 and receive the shank of the hollow rivets 41. The bottom of the base member 30 is provided with a pair of channels 43 and 44, and the end member 31 is provided with an opening 45 extending from exterior thereof through the end member 31.

The end member 31 is provided with a reentrant bore 46 extending partially therethrough as shown in Figure 4, and the end member 32 is provided with a larger bore 47 aligned with the bore 46 but extending completely through the end member 32.

Mounted in the channel 43 is a conductor 48, and mounted in the channel 44 is a resistance element 49. The conductor 4S is preferably in the form of a thin strip of low-contact resistance platinum alloy sheet metal bent into a substantially U-shaped cross section so as to present a fold line or bend 50 which is perfectly straight and level from one end to the other and which lies entirely within a single plane. The resistance element 49 is a liat coil 51 of line resistance wire wound on a core 52. Three electric wires or conductors 53, 54 and 55 extend through the opening 45 and into the interior of the base member 30. The wire 53 is electrically connected to the con- .ductor 48. The wire 55 is connected as by soldering to a hollow rivet 56. There are two such hollow rivets, one at each end of the resistance element 49, and each of them is attached to the resistance element in the same manner. T he wire 55 is thus attached to one end of the coil 51 by means of the hollow rivet 56, and the hollow rivet 57 is attached to the other end of the coll 5l.

Referring to Figure 9, it will be noted that the hollow rivets 57 and 56 have wires attached thereto as by soldering as at 58, and one turn 61 of the wire making up the coil 51 is aliixed in an annular channel 60 formed in a boss 59 carried by the hollow rivets. The hollow rivet 57 is thus attached to a wire 62, which wire 62?, leads from the hollow rivet 57 across the base member 36 to the channel 43 where it passes back through said channel be tween the flanges of the U-shaped conductor 4d. The wire 62 is an extension of the wire 54.

A shaft 63, having one end thereof seated in the bore 46 and the other end positioned in the bore 47 is provided, having a slotted head 64. The shaft 63 has an enlarged portion 65 seated in the bore 47 which is provided with an annular groove 66, and a pin 67 passes through the end member 32 and prevents endwise movement of the shaft 63 but permits rotation thereof. The shaft 63, intermediate its ends, is provided with a screw thread 68 which is precisioned to a high degree of uniformity, and a block or slider 69 which is tapped with a similar Athread 79 is adapted to be mounted on the shaft 63 as indicated. The block 69 is provided with a pair of grooves 71 and 72 at one end thereof on either side, and the side walls 73 and 74 and the top 75 of the block 69 are adapted for close sliding contact with the inner -walls of the anges 39 and the web 38 of the cover '37 which thus restrain theblock 69 from any turning movement on the shaft 63. A contact spring element 76 is provided, having a pair of legs 77 and 78 adapted to engage in the grooves 71 and 72 and having a pair of spring contact arms 79 and 80 and bridging portion 31. The spring arm 79 is adapted to engage resistance element 49 while the spring arm 80 is adapted to engage conductor 48.

From the foregoing description, it will be apparent that turning of the shaft 63 as, for example, by inserting a screw driver in the slotted head 64, will cause the block 69 to travel longitudinally of the shaft 63 and thus move the spring arms 79 and 80 respectively along the surface of the resistance 4element 49 and the conductor 4S, thus varying the resistance of the circuit.

As shown in yFigure 2, a plurality of variable resistors, constructed in accordance with the above-described specication, can be mounted in fixed yposition upon a pair of parallel posts 32 and 83, which, in practice, has been found a convenient method of assembly,

Referring now more particularly to Figures 1.6 and 17, there is shown `a resistance element 84 constructed in acoordance with the above-described specication but having a tapped hole 85 in the end member 31. An auX- iliary resistor element 86 having a plastic body 87 is attached to the resistor 84 by means of a screw 88 received in the tapped hole 85. The body 87 is provided with an opening 89 in which is positioned one or more resistors 90. One or more of the wires 53, 5d or'SS may be attached to one or more of the resistors 90 which in turn are connected to further lead wires 91.

Referring to Figure 20, there kare .shown two circuits variously labeled A and B. The circuit A is the circuit of the above-described device. It is obvious that circuit B can. be achieved by attaching one of the lead wires to another resistance. Thus with Ithe device just described, there is permitted a precise adjustment of the resistance or" a circuit over a small portion only of the total resistance or voltage involved. i Circuit B is particularly well suited for use in a Wheatstone bridge, serving as two arms of the bridge with a movable contact permitting an extremely precise adjustment of the balancing of the bridge.

Referring now more particularly to Figures ll through i5, there is shown an alternative embodiment of the invention employing a molded plastic base 92 and a metallic cap 93. The molded plastic base is shown in perspective in. Figure 14 and includes a pair of channels 94 and '95 for respectively housing the conductor element 96 .and the resistor element 97 as showvn in Figure 13. The grooves 94 and 95 communicate with an enlarged groove 98 which accommodates the lead wires 99.

ln this embodiment ot' the invention, the cap 93 includes at each end inwardly turned walls 10i) and upstanding walls 1111. Each of the walls 101 is provided with a hole 102 through which pass the reduced ends of the shaft 103. The shaft 103 is threaded as indicated, and one end thereof is slotted as at 104. The end 105 of the cap 93 is provided with an enlarged holeto permit access to the slotted end 104 of the shaft 103 by a suitable tool, such as a .small screw driver, for `turning the shaft 1413. A block 107, in all respects similar to the block 69 and carrying a contact spring 108 similar to the contact spring 76, is mounted upon the shaft 103. In all other respects, this embodiment of the present invention is the same as the rst described embodiment. The virtue of this particular embodiment of the present invention liesparticularly in the fact that it permits an easier fabrication of parts due to the ability to assemble the cap, Shaft and block as a unit, while the resistor and conductor are assembled as a unit in the base 92, the lead wires lying in thegroove 98 rather than passing through a hole, :and the entire assembly can then `be merely snapped `together,andsecured by the. hollow rivets.

While there has been described what are at present considered the preferred embodiments of the present invention, it will be appreciated by those skilled in the art that various changes and modifications can be made therein without departing from the essence of the invention, and it is intended to cover herein all such changes and modications as come within the true spirit and scope of the appended claims.

I claim:

l. A variable resistor comprising: a housing member having two opposite substantially flat side portions; a resistance element and a conductor mounted in said housing member; a slider mounted in said housing; screw means engaging said slider and adapted upon turning to cause longitudinal travel of said slider; means restraining said slider against rotation; spring contact members on said slider engaging said resistance element and said conductor, means for making external connections to said resistor and said conductor, including an opening parallel to said two flat side portions through vone end of said housing member, and an opening substantially perpendicular to said flat side portions to permit close and rapid assembly with other variable resistors.

2. A variable resistor comprising: a housing member having two opposite substantially flat side portions; a resistance element mounted in said housing member; a slider mounted in said housing; screw means engaging said slider and adapted upon turning to cause longitudinal travel of said slider; means restraining said slider against rotation; a contact member on said slider engaging said resistance element; means restraining said screw means against longitudinal movement in said housing member, means for making external connections to said resistor, including an opening parallel to said two ilat side portions through one end of said housing member, and an opening substantially perpendicular to said flat side portions to permit close and rapid assembly with other variable resistors.

3. A variable resistor comprising: a housing comprising a base member and a cap; a resistance element mounted in said housing; a slider mounted in said housing; screw means engaging said slider and adapted upon turning to cause longitudinal travel of said slider, means restraining said slider against rotation; a contact member on said-slider engaging said resistance element; and a pair of spaced hollow rivets, each extending through said base member and said cap and securing said cap to said base member, whereby a plurality of like resisltors may be .assembled upon parallel posts extending through said hollow rivets.

4. A variable resistor comprising: a base member of molded plastic material; said base .member having a pair of parallel longitudinal grooves therein and a pair of spaced upstanding portions; a resistance element mounted in one of said grooves; a conductor mounted in the other of said grooves; screw means mounted between said spaced portions; means engaging said screw means to prevent longitudinal movement thereof while permitting rotation thereof; a slider having a threaded engagement with said screw means; spring contact members carried by said slider and engaging said resistance element and conductor; and a cap mounted on said base member, enclosing said resistor and restraining said slider against rotation whereby turning of said screw means causes said spring contact members to travel over said resistance element and said conductor.

5. A variable resistor as set forth in claim 4 including .a separate case; means for attaching said case to said v,pair of;parallellongitudinal grooves therein and a pair of spaced upstanding portions; a resistance element t mounted in one of said grooves; a conductor mounted in the other of said grooves; screw means mounted between said spaced portions; means engaging said screw means to prevent longitudinal movement thereof while permitting rotation thereof; a slider having a threaded engagement with said screw means; contact members carried by said slider and engaging said resistance element and conductor; a cap mounted on said base member, enclosing said resistor and restraining said slider against rotation whereby turning of said screw means causes said spring contact members to travel over said resistance element and said conductor; and said cap being secured to said base member by a pair of spaced, parallel hollow rivets.

7. A variable resistor comprising: a base member of molded plastic material having a pair of parallel longitudinal grooves therein; a resistance element in one of said grooves; a conductor in the other of said grooves; a cap engageable with said base element; said cap providing a pair of spaced walls; screw means mounted between said spaced walls; a slider having a threaded engagement with said screw means and being in sliding contact with said cap whereby said slider is restrained against rotation; contact means carried by said slider and adapted to engage said resistance element and said conductor, whereby on rotation of said screw means said spring contact means travels over said element and conductor.

8. A variable resistor comprising: a base member having a pair of longitudinal grooves therein and a pair of upstanding portions at opposite ends thereof; a resistance element mounted in one of said grooves; a conductor mounted in the other of said grooves, said conductor comprising a thin strip of sheet metal bent into an inverted U-shaped cross section; a terminal wire connected to one end of said resistance element and passing through said other groove underneath said U-shaped conductor strip to the opposite end of said base member, screw means mounted between said upstanding end portions; means engaging said screw means to prevent longitudinal movement thereof while permitting rotation thereof; a slider having threaded engagement with said screw means; spring contact members carried by said slider and wiping on said resistance element and the crest of said U-shaped conductor; and means for restraining said slider against rotation whereby turning of said screw means causes said spring contact members to travel over said resistance element and said conductor.

9. A variable resistor comprising: a base member having a pair of longitudinal grooves therein and a pair of upstanding portions at opposite ends thereof; a resistance element mounted in one of said grooves; a conductor mounted in the other of said grooves, said conductor comprising a thin strip of sheet metal bent into an inverted U-shapedv cross section; a terminal wire connected to one end of said` resistance element and passing through said other groove underneath said U-shaped conductor strip to the opposite end of said base member; screw means mounted between said upstanding end portions; means engaging said screw means to prevent longitudinal movement thereof while permitting rotation thereof; a slider having threaded engagement with said screw means; spring contact members carried by said slider and wiping on said resistance element and the crest of said U-shaped. conductor; a cap mounted on said base member, enclosing said resistor and restraining said slider against rotation, whereby turning of said screw means causes said spring contact members to travel over said resistance element and said conductor; and a pair of spaced hollow rivets extending through said base member and said cap and securing said cap to said base member, whereby a plurality of like resistors may be assembled upon parallel posts extending through said hollow rivets.

l0. A variable resistor comprising: a base member having a pair of longitudinal grooves therein and a pair of upstanding portions at opposite ends thereof; a resistance element mounted in one of said grooves; a conductor mounted in the other of said grooves, said conductor comprising a thin strip of sheet metal bent into an inverted U-shaped cross section; a terminal wire connected to one end of said resistance element and passing through said other groove underneath said U-shaped conductor strip to the opposite end of said base member; screw means mounted between said upstanding end portions; means engaging said screw means to prevent longitudinal movement thereof while permitting rotation thereof; a slider having threaded engagement with said screw means; spring contact members carried by said slider and wiping on said resistance element and the crest of said U-shaped conductor; means for restraining said slider against rotation; and a pair of parallel apertures extending transversely through said upstanding end portions to one side of said screw means, said apertures being adapted to receive parallel mounting posts, whereby a` plurality of like resistors may be assembled upon said mounting posts.

ll. A variable resistor comprising: a base member' having a pair of upstanding portions at opposite endsY thereof; a resistance element and a conductor mounted side by side on said base member; screw means rotatably mounted between said upstanding end portions; means engaging said screw means to prevent longitudinal movement thereof while permitting rotation thereof; a slider having threaded engagement with said screw means; spring contact members carried by said slider and wiping on said resistance element and conductor; means restraining said slider against rotation, whereby turning of said screw means causes said spring contact members to travel over said resistance element and said conductor, and means for mounting said resistor, including apertures extending transversely thru said upstanding end portions of said base member to receive parallel mounting posts.

l2. A variable resistor comprising: a base member having a bottom portion and upstanding portions at opposite ends thereof; a resistance element mounted on said base member; screw means rotatably supported between said upstanding end portions; a slider having threaded engagement with said screw means; a contact member carried by said slider and wiping on said resistance element; a U-shaped metal cover wrapped around three sides of said body to enclose said resistor, and means forl mounting said resistor including apertures extending transversely through said upstanding end portions of said base member and through the sides of said U-shaped metal cover, and hollow rivets extending through said apertures and securing said cover to said base member, said hollow rivets being adapted to receive parallel mounting posts,

whereby said resistor can be quickly and easily assembled in side by side relationship with other like resistors.

13. A. variable resistor comprising: a housing memben. a resistance element mounted therein, a slider mounted.

in said housing, screw means engaging said slider and adapted upon turning to cause longitudinal travel of said slider, means restraining said slider against rotation, a.

Contact member on said slider engaging said resistance element, a separate housing member, means for attach-v ing said separate housing member to said housing member, a resistance element in said separate housing member, and means for attaching said resistance element in.

said separate housing member with the resistance element` in said housing member.

14. A variable resistor comprising a housing having two opposite, substantially at and parallel sides, a resistance element mounted in said housing, a slider movable longitudinally of said resistance element and having a contact wiping thereon, screw means engaging said slider and adapted upon turning to move the slider along the length of said resistance element, an opening extending transversely through said housing perpendicular to said flat sides to receive a mounting post, so as to permitclose and rapid assembly with other variable resistors., and terminal means connected to said resistance element and electrically connected to said contact and passing through another side of said housing.

l5. A variable resistor comprising a housing having twoV opposite, substantially flat and parallel sides, a resistance element mounted in said housing, a slider movable longitudinally of said resistance element and having a contact wiping thereon, screw means engaging said slider and adapted upon turning to move the slider along the length of said resistance element, one end of said lead screw projecting through one end of said housing for adjustment control, an opening extending through said housing perpendicular to said at sides to receive a mounting post, and terminal means connected to said resistance element and electrically connected to said contact and passing through an aperture in the other end of said housing.

16. A variable resistor comprising a housing, a resistance element mounted on said housing, a lead screw rotatably supported parallel to said resistance element, a slider engaged by said lead screw and movable longitudinally of said resistance element when the lead screw is turned, a contact on said slider engaging said resistance element, a cover mounted on said housing to enclose said lead screw, slider and resistance element said housing and said cover cooperating to form a conduit in one side of said housing, and terminal means electrically connected to said resistance element and to said contact and passing out or" said resistor thru said conduit between said cover and said housing.

17. A variable resistor comprising a housing having a resistance element mounted thereon, a rotatable lead screw disposed parallel to said resistance element, a slider engaged by said lead screw and movable longitudinally of said resistance element when the lead screw is turned, a contact on said slider engaging said resistance element and a cap secured to said housing to enclose said lead screw, slider and resistance element, said cap having an end portion which is bent downwardly parallel to the ends of said housing and terminates in a tab that is bent inwardly and then turned upwardly, said upwardly turned tab being apertured to receive and rotatably support one end of said lead screw.

18. A variable resistor, as defined in claim 17 wherein one end of said lead screw is shaped to receive an adjusting tool, said one end of said lead screw being disposed within the space between said tab and said one end portion of said cap, and said one end of said cap being apertured to provide access to said one end of said lead screw for adjustment purposes.

19. A variable resistor comprising a base member having a resistance element and a conductor element mounted thereon, a rotatable lead screw disposed parallel to said elements, a slider engaged by said lead screw and movable along the length thereof when said lead screw is rotated, a. contact member on said slider wiping on said resistance element and conductor element, and a terminals means at one end of said base member connected to the adjacent ends of said conductor element and said resistance element, said terminal means including a wire connected to the other end of said resistance element and passing underneath one of said elements to said one end of said base member.

20. A variable resistor comprising a housing composed of a base member and a cover which cooperate to form an enclosed cavity, said housing being an elongated body of substantially uniform cross section the length dimension of said housing being substantially greater than either the width or height dimensions, a long slender resistance element disposed within said cavity and extending longitudinally of said housing, an adjusting screw rotatably mounted within said cavity and having a head exposed through an aperture in one end of said housing to provide for external adjustment thereof, a slider engaged byv said adjusting screwy and having a contact wiping on said resistance element, said slider being movable lengthwise of said resistance element responsive to rotation of said adjusting screw and restrained against rotation, said resistor being mounted so that said one end of said housing with said exposed head of the adjusting screw is presented, whereby the minimum area of the resistor is presented for adjustment purposes, said resistor being adapted to be assembled in juxtaposition with other like resistors to group the maximum number of resistors in a given space with said screw heads immediately accessible for adjustment purposes, and terminal means electrically connected to said resistance element and to said contact.

21. A precision miniature resistor comprising a housing consisting of a base member having upstanding portions at the ends thereof and a cap, said housing having a pair of opposed parallel at sides, a resistance element and a conductor strip mounted side by side on said base member between said upstanding portions, a slider having a contact thereon wiping on said resistance element and said conductor strip, said slider being of block form having at least one` extended side cooperating with said housing to restrain the slider against rotation, self locking means for accurately shifting said slider along the length of said resistance element and conductor and holding the same against displacement so that the resistor can readily be adjusted to give precise and reproducible electrical settings, said means comprising a screw journaled in said upstanding end portions of said base member and having threaded engagement with said slider block, said screw having a head shaped to receive an adjusting tool, and said head projecting through one end of said housing, means for restraining longitudinal movement of said screw while permitting rotation thereof, and means for mounting said resistor in closely stacked array 'with other like resistors, comprising a pair of spaced apertures extending through said housing perpendicular to said parallel at sides to receive mounting posts.

22. A variable resistor comprising a base member having upstanding portions at opposite ends thereof, a resistance element mounted on said base member, screw means rotatably supported between said upstanding end portions, a slider having threaded engagement with said screw means, a contact member carried by said slider and wiping on said resistance element, a U-shaped cover wrapped around three sides of said body to enclose said resistor, means for mounting said resistor including apertures extending transversely through said upstanding end portions of said base member and through the sides of said U-shaped cover, said apertures being adapted to receive parallel mounting posts, whereby said resistor can be quickly and easily assembled in side by side relationship with other like resistors, and means securing said cover to said base member.

References Cited in the le of this patent UNTTED STATES PATENTS 2,357,433 Side Sept. 5, 1944 2,439,069 Anderson Apr. 6, 1948 2,506,482 Batchellor May 2, 1950 2,712,583 Mucher July 5, 1955 FOREIGN PATENTS 264,626 Italy May 4, 1929 551,350 Germany May 12, 1932 645,898 Great Britain Nov. 8, 1950 

